This application claims the priority of German Patent Application, Ser. No. 101 06 915.4, filed Feb. 15, 2001, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a suspension for a motor vehicle.
The suspension of the chassis of a motor vehicle is used to couple the vehicle body and the wheel support assembly in an elastic manner. The suspension is intended to insulate the vehicle body from high-frequency vibrations of the wheels and at the same time flexes to absorb the long-wave road surface contour. Various suspension systems are known in the art. Besides the use of leaf springs, which find application mostly in trucks, it is also known to employ torsion bar springs, pneumatic springs as well as silent blocks. Oftentimes, conventional suspension systems employ compression-type coil springs which are able to realize progressive, degressive or linear spring rate through provision of different wire sizes and different configurations. A particular space-saving configuration can be implemented, when using barrel springs which have windings which are nested within one another during compression. In addition to these types of coil springs, called load-carrying springs, auxiliary slave springs have been used to provide a stop in parallel disposition to the load-carrying spring. Typical materials for slave springs are rubber or cellular polyurethane elastomers. The slave spring may also operate as spring buffer to prevent an inadvertent bottoming of the coil spring. Conventionally, the slave springs are arranged outside the load-carrying spring and held in a cup-shaped receptacle.
It is also known to use a spring plate to correctly position the load-carrying spring, and to arrange a spring washer between the load-carrying spring and the spring plate. The spring washer is normally made of rubber, but may also be made of galvanized metal sheet or surface-coated metal sheet, and is used as sacrificial anode to prevent corrosion of the load-carrying spring.
When arranging the slave spring in coaxial relationship to the load-carrying spring, the installation is complex because of the need to place in a tight space three different components, i.e., first, the cup-shaped receptacle with the slave spring for attachment to the spring plate, second, the spring washer arranged between the spring plate and the load-carrying spring, and third, the actual load-carrying spring. While the slave spring and the receptacle may be constructed to form a pre-fabricated unit, the load-carrying spring and the spring washer constitute single parts which only in the spring-loaded installation stage are correctly positioned. Handling of the single parts is difficult during installation, especially when taking into account their considerable weight.
It would therefore be desirable and advantageous to provide an improved suspension which obviates prior art shortcomings and which is easy to handle during installation and allows use of light-weigh materials.
According to one aspect of the present invention, a suspension includes a load-carrying spring having one end indirectly supported via a first spring washer by a vehicle body component and another end indirectly supported via a second spring washer by a component of the wheel support assembly of a motor vehicle; a cup-shaped receptacle disposed at the one end of the load-carrying spring; an abutment disposed at the other end of the load-carrying spring and having a stop surface; and a slave spring disposed in coaxial relationship to the load-carrying spring and having one end received in the receptacle and another end intended for engagement with the stop surface of the abutment, wherein the receptacle and/or the abutment has a radially outwardly extending support ring for at least partially engaging behind the proximal one of the first and second spring washers at a side distal to the load-carrying spring.
For convenience and sake of simplicity, the following description may on occasion refer only to the area of the receptacle, when in fact the connection of the abutment on the confronting side is substantially a mirror image of the connection and placement of the receptacle about an imaginary horizontal medial plane. Thus, although the suspension may be described with respect to only the area of the receptacle, it will be understood that the same components of the suspension may also be duplicated on the side of the abutment, or vice versa.
The present invention resolves prior art problems by providing the receptacle and/or the abutment with a support ring to engage behind the respectively proximate spring washer on the load-carrying spring distal side, so that the receptacle with the slave spring and the one spring washer and/or the abutment and the other spring washer form a pre-fabricated unitary structure, respectively. The final installation can thus cope with fewer components to thereby significantly facilitate the assembly. Of course, the receptacle as well as the abutment may each be provided with such a support ring.
The suspension according to the present invention is advantageous in particular in those situations, when the load-carrying spring is configured as a barrel spring with reduced winding diameter at the ends. In this case, the support ring can be configured with an outer diameter which is only slightly greater than the winding diameter of the end turn to ensure a secure clamping of the spring washer between the load-carrying spring and the support ring. The use of support rings with comparably smaller outer diameter saves material and thus weight and as a result leads to reduced fuel consumption.
According to another feature of the present invention, the spring washers may each have a collar to bear radially outwards upon the receptacle and/or the abutment, respectively, and points in a direction of the load-carrying spring, for correctly positioning the respective end of the load-carrying spring in a radial direction in cooperation with the receptacle and/or the abutment, respectively. The receptacle thus assumes several functions. The load-carrying spring indirectly rests via the spring washer against the support ring of the receptacle whereby the receptacle at the same time correctly positions the one end of the load-carrying spring in radial direction. The need for central guide pins or the like, as required for barrel springs, is eliminated. The provision of the collar, directed toward the load-carrying spring, prevents wear and noise generation between the load-carrying spring and the receptacle. The collar has a height which corresponds suitably at least to the wire diameter of the end turn of the winding. The abutment assumes the same functions as the receptacle in concert with the other spring washer and also provides a correct disposition of the load-carrying spring.
Apart from the fact that the spring washer at the side of the receptacle and the slave spring may form a prefabricated unitary structure, it is also suitable when this unitary structure is captivated by the load-carrying spring. This can be realized by providing the collar with a radially inwardly pointing undercut for engagement of an end turn of the load-carrying spring. As a consequence of the spring force applied by the load-carrying spring, the end turn is snapped in forced engagement with the undercut. Thence, the collar and thus the spring washer assembly are pressed radially on the outside against the receptacle so that these components can be installed as a whole. The undercut can be so positioned that the spring washer is also pressed in axial direction against the support ring of the receptacle by the load-carrying spring.
In the event, the spring washer is made of rubber or of a highly compliant elastomer, the provision of an undercut of the collar may be insufficient to properly secure load-carrying springs of substantial weight, the receptacle and/or the abutment may have an outer perimeter formed with an impression in an area of the collar. When the load-carrying spring is pre-assembled with the receptacle and the abutment, the last turn of the load carrying spring is able to press the collar into the impression that serves as undercut.
Wheel support components, such as, e.g., vehicle axles, may have several degrees of freedom. Thus, it is not always ensured that the slave spring strikes against the stop surface of the abutment with coincident longitudinal center axes, i.e. that the end faces of the slave spring and the abutment contact one another in parallel relationship. Thus, in accordance with another feature of the present invention, the stop surface of the abutment is defined by a surface normal which deviates from the longitudinal center axis of the load-carrying spring. In a relaxed state, the longitudinal center axis of the load-carrying spring coincides with the longitudinal center axis of the slave spring. In the event the suspension is compressed in an oblique way, the surface normal of the stop surface is so oriented in dependence on the vehicle type and the configuration of the frame that the surface normal substantially coincides with the longitudinal center axis of the load-carrying spring during impact of the slave spring. Thus, almost exclusively normal forces act in the slave spring. Bending forces, which can influence the spring rate, are eliminated. As a consequence, the service life of the slave spring is enhanced and the overall suspension is better balanced.
Of course, it is also possible, to provide the end face of the slave spring, confronting the stop surface of the abutment, with a respective inclination to ensure a substantially parallel impacting of the slave spring upon the stop surface.
According to another feature of the present invention, the stop surface of the abutment may be curved concavely. This may be suitable in particular when the slave spring is made of rubber or polyurethane elastomers, because an additional centering upon the surface normal of the stop surface is realized.
Whereas conventional abutments are typically made of steel, according to another feature of the present invention, the receptacle and/or the abutment can be made of plastic, resulting in a significant weight reduction.
According to another feature of the present invention, the abutment may have a mounting pin for engagement in an opening of the vehicle body or the wheel support assembly. The mounting pin engages substantially free of play into the opening to ensure a reliable guidance of the abutment and thus of the load-carrying spring. Suitably, the mounting pin may have an outer periphery formed with at least one clamping rib so as to firmly retain the abutment in the opening. In particular, when the abutment is made of a material which is softer than the material of the involved wheel support component or the vehicle body component, such as e.g. plastic, the clamping rib may wear off during insertion in the opening to thereby ensure a firm seat of the mounting pin and thus of the abutment in the opening.
In addition to or as an alternative to the provision of one or more clamping ribs, the mounting pin may have several resilient clamping hooks with a radially outwardly directed nose for engagement behind edges of the opening. The nose is suitably formed with a slanted surface for allowing the hook to slide during installation into the opening. The spring-loaded hooks snap behind the edges of the opening, which are facing away from the load-carrying spring, in the locked position, so that the abutment is firmly clamped to the vehicle body or the wheel support assembly.
When the opening has a circular configuration, the installation of the abutment requires a correct disposition of the stop surface of the abutment. This can be realized by securing the abutment against executing a rotational motion, e.g. by providing the mounting pin with an alignment rib on its outer periphery for engagement in a complementary recess on the edge of the opening. Of course, the reverse configuration is conceivable as well, i.e., to provide the mounting pin with a circumferential recess for engagement by a complementary protrusion projecting from the edge of the opening. Other anti-rotation configurations are certainly possible as well and are considered covered by the present invention, such as, e.g., the provision of a particular shape of the opening that allows only one placement of the abutment. Other anti-rotation configurations may be disposed outside the opening, for example, the provision of a pin arranged on the support ring for engagement in an additional bore in the wheel support component or the vehicle body.
The overall weight can be further reduced by making the abutment as an injection-molded part of plastic, with the mounting pin constructed as a hollow pin. The mounting pin may have a diameter which is different from the outer diameter of the abutment, whereby the diametrical deviation can be bridged by a number of reinforcing ribs. This further reduces the weight. An even further weight reduction can be realized through recessing the receptacle at the side facing away from the load-carrying spring.
Weight can also be decreased by providing the spring washers on the side which is distal to the load-carrying spring with a latticed structure along certain areas. Through varied configuration of the latticed structure, the spring rate of the suspension can be additionally influenced. Possible parameters include number, disposition and geometric configuration of the indentations within the latticed structure, and chosen material.
According to another feature of the present invention, the load-carrying spring distal side of the spring washers and the load-carrying spring distal side of the support ring extend in a same plane. Thus, the spring washer affords space for the support ring, whereby the afore-described latticed structure extends suitably from the outer edge of the support ring to the outer edge of the spring washer.
According to another feature of the present invention, the load-carrying spring is configured as a barrel spring and has a winding diameter which is smaller at the ends of the load-carrying spring.
According to another feature of the present invention, the load-carrying spring has an inconsistent wire diameter. Suitably, the wire diameter decreases towards the ends. Apart from the variation of the winding diameter and the wire diameter, the spring characteristic of the suspension can be influenced also by the configuration of the slave spring. When the slave spring is made of solid material, in particular of rubber or polyurethane elastomer, the spring characteristic is somewhat steeper, although the steepness could be flattened through material-saving construction, in particular through provision of a substantially cylindrical hollow spring. The slave spring may have a barrel-like cross section or cylindrical cross section or also a wedge-shaped configuration. The actual configuration can be best suited to the desired spring properties under consideration of the height and diameter of the receptacle or the ratio of height and diameter of the receptacle.
The receptacle may have one or more circumferential reinforcing grooves and may terminate in an outwardly pointing edge to prevent damage to the slave spring, when the slave spring is made of elastomer and compressed obliquely.